MOSFET with reduced short channel effect

A semiconductor switching device comprising:

• source and drain regions formed in a semiconductor material;
• a gate insulating film formed on a semiconductor surface between said source region and said rain region;
• a gate electrode formed on said gate insulating film;
• and
• a semiconductor layer lying beneath said gate insulating film and sandwiched between said source region and said drain region, said semicodnuctor layer being made up of a first layer and a second layer, said first layer being contiguous to said gate insulating film and opposite in conductivity type to said source and drain regions, said second layer lying beneath said first layer and having the same conductivity type as said source and drain regions, the length of said second layer between said source region and said drain region being greater than the length of said first layer between said source region and said drain region,
• wherein said source region, said drain region and said semiconductor layer are provided on an insulating material,
• wherein a depletion layer due to a PN junction between said first layer and said second layer is extended to said insulating material, and
• wherein said first layer has an electrical potential substantially equal to an electrical potential of said source region.

A semiconductor switching device comprising:

• source and drain regions each having a firs conductivity type formed on a semiconductor substrate opposite in conductivity type to said source and drain regions;
• a gate insulating film formed on a semiconductor surface between said source region and said drain region;
• a gate electrode formed on said gate insulating film;
• and
• a semiconductor layer lying beneath said gate insulating film and sandwiched between said source region and said drain region, said semiconductor layer being made up of a first layer and a second layer, said first layer being contiguous to said gate insulating film and opposite in conductivity type to said source and drain regions, said second layer lying beneath said first layer and having the same conductivity type as said source and drain regions, the length of said second layer between said source region and said drain region being greater than the length of said first layer between said source region and said drain region, wherein first layer is not isolated from said substrate.